1. Technical Field
The present invention relates to a throttle opening detection device for detecting opening of a throttle in a motorcycle or other vehicle with a rotatable acceleration grip.
2. Background Art
In a motorcycle, an acceleration grip is mounted on a handle bar. When a rider rotates the acceleration grip in the circumferential direction, a throttle valve mounted on an internal combustion engine performs an open/close operation along with such rotation of the acceleration grip.
It is necessary to control the open/close operation of the throttle valve in such a manner that an open/closing amount of the throttle valve corresponds to a rotational amount of the acceleration grip. Accordingly, there has been known a technique where a throttle opening detection device for detecting a rotational amount of an acceleration grip is mounted on a handle bar of the motorcycle or other vehicle.
This type of throttle opening detection device includes a rotor which is rotated in an interlocking manner by manipulation of the acceleration grip. As shown in FIG. 6 of JP-A-2006-112284, for example, a plurality of magnets are mounted on the rotor. Accordingly, positions of the plurality of magnets are changed following the rotation of the rotor.
The throttle opening detection device further includes a magnetic sensor such as a Hall element. The magnetic sensor outputs an electric signal corresponding to a magnetic flux density of the magnet at a detecting position. A rotational amount (rotational angle) of the rotor and, eventually, a rotational amount of the acceleration grip can be obtained based on the electric signal output by the magnetic sensor.
As shown in FIG. 6 of JP-A-2006-112284, the magnetic sensor is conventionally arranged outside the rotor in the radial direction. The reason is as follows. Assuming that the magnets and the magnetic sensor have such a positional relationship, when the magnetic flux density corresponding to a rotational angle of the rotor is plotted on a graph, the correlation becomes linear and hence, an electric signal which the magnetic sensor outputs and, eventually, a rotational amount of the acceleration grip can be easily evaluated with high accuracy.
However, due to such a constitution, a location where the magnetic sensor is arranged is limited and hence, the degree of freedom in the layout of arrangement of other parts is decreased. Further, it is difficult to avoid making the throttle opening detection device large in size along the radial direction of the rotor.